The invention pertains to the transport of articles along a predetermined path while reducing to an absolute minimum any resistance to such movement of the article.
It frequently occurs in a manufacturing facility that a flat workpiece must be transported a distance from a machine and then dropped at a specific location to form a stack. For example, sheet material may be fed into a press where it is sheared into panels. The panels are removed from the machine, conveyed away from the machine, and then stacked on a pallet or the like.
It can be appreciated that the most convenient way of performing this operation is by suspending the panels from the lower span of the conveyor and then releasing the panel when it arrives at the stack. To this end it has been the practice to provide a continuous loop belt type conveyor with a series of electromagnets fixedly mounted within the loop and in engagement with the inner surface of the lower span of the belt. The belt is driven relative to the electromagnets. As the panels are removed from the machine they are transferred to the lower span of the conveyor where the energized electromagnets act on them to draw the panels against the moving belt and retain them there while the belt moves the panel to the stacking location where they are released from the conveyor by the electromagnets to drop onto the stack.
In some installations the electromagnets are replaced by vacuum assemblies which function through the conveyor belt to apply a vacuum for retaining the workpieces against the surface of the belt for movement therewith.
In these prior art constructions the conveyor belt is held against the surface of either the magnets or the suction devices while it is moving. This creates friction that must be overcome by increased power for driving the conveyor and which also causes undue wear and tear on the conveyor belt.
In the presently available stacking systems employing a conveyor to transport the article to the stack, the article is released from the belt while the belt is moving. As a result, after the article is released from the belt it does not drop in a direct vertical path but continues to move forwardly as well. Therefore, in order to position the article on the stack, the receiving platform is provided with a backstop to stop the forward movement of the article and position it on the stack. Such bumping of the article against the backstop has a tendency to mar the article. Irregular articles are also difficult to stack with this system.
Another potential source of damage to the article being transported lies in the fact that the article must be transferred to the conveyor while the belt is moving, to produce substantial abrasion between the belt and article.
Another disadvantage in the prior art structures is that the speed of the belt cannot be readily varied. Once its velocity is established it will remain uniform during the operation and it dictates the spacing of the parts on the conveyor.